Paper bags having leak-proof seams



Dec. 19,1967 P. J. DE STEFANO ETAL 3,353,903

PAPER BAGS HAVING LEAK-PROOF SEAMS Filed March 31, 1966 4 Shets-Sheet l FIG. 40 FIG 3 34 26 4a IN VENT ORS Bur/re P Lo/rey Pa/r/c/r J De S/efano Dec. 19, 1967 P. J. DE STEFANO ETAL PAPER BAG'S HAVING LEAK-PROOF SEAMS 4 Sheets-Sheet 2 Filed March 31, 1966 FIG. 8

l jl'lllIIIL-ll w m m 6 m H a P.

Patric/r J. De S/efano AGENT Dec. 19, 1967 P. J. DE STEFANO ETAL 3,

PAPER BAGS HAVING LEAK-PROOF SEAMS Filed March 31, 1966 4 Sheets-Sheet 3 93 FIG. /3

HG I70 INVENTORS Bur/re P L 0/re Pcz/n'c/r J. De S/efano AGT Dec. 19, 1967 P. J. DE STEFANO ETAL PAPER BAGS HAVING LEAK-PROOF SEAMS 4 Sheets-Sheet 4 Filed March 31, 1966 FIG. 22

I INVENTORS /26 BY W AGENT United States Patent 3,358,903 PAPER BAGS HAVING LEAK-PROOF SEAMS Patrick J. De Stefano and Burke P. Lokey, Metairie, La., assignors to West Virginia Pulp and Paper Company, New York, N.Y., a corporation of Delaware Filed Mar. 31, 1966, Ser. No. 539,036 4 Claims. (Cl. 229-53) ABSTRACT OF THE DISCLOSURE A leak-proof paper bag having a seamless bottom and a compound seam along each side, each compound seam being formed of an adhesively joined primary seam and at least one adhesively joined secondary seam, the adhesive of each primary seam being exposed to the interior of the bag and the adhesive of each secondary seam being shielded from the interior of the bag by the primary seam.

This invention relates to paper bags having leak-proof capabiilty. It more particularly relates to paper bags of end-over-end construction, having a seamless bottom and a leak-proof compound seam along each side. It specifically relates to bags of this type in which each compound side seam is cooperatively formed by an adhesively joined primary seam that is in contact with bag contents and an adhesively joined secondary seam that is shielded from contact with bag contents by the primary seam.

Leak-resistant and leak-proof paper bags, having a capacity of twenty gallons, for example, are particularly useful for refuse collection in restaurants, airplanes, and other food-dispensing locations. Moreover, bags having truly leak-proof characteristics are greatly needed in hospitals where leakage of infectious material must be completely avoided.

The prior art shows that end-over-end paper bags which have a side seam along each side gusset and a seamless bottom have been known for many years. For example, J. McCullough in US. 224,934 showed a bag of this type which has overlapped side seams of an unprotected shearjoint type that are formed by reverse folding of an extended flap along each side of one bag wall and applying to this flap a single line of adhesive from bottom fold to end of flap. J. C. Hellema in US. 2,203,726 also described a bag of this sort with seams having unprotected shear joints and a seamless bottom having triangular.

pockets glued thereto. G. O. Blowers in U.S. 286,896 and W. P. Flowers in U .S. 775,268 described bags having seamless bottoms, which are inwardly folded when flat, and side seams formed from unprotected peel joints which project inwardly. A. C. Campbell in U.S. 227,147 showed a bag having a seamless, inwardly-folded bottom and outwardly folded sides with shear-joint side seams.

A peel joint is herein defined as an adhesive juncture of juxatposed bag walls that is subject to being peeled open by a transversely-applied force. A shear joint is herein defined as an adhesive juncture of juxtaposed bag walls that is subject to rupture in shear by a transverselyapplied force.

These bags and others in the prior art have difiiculty in maintaining a liquid-tight seal. There is a pronounced tendency to leak through random openings in the side seams, which are under transverse tensile stresses, and along the bottom corners at the intersections of the bottom fold and the side seam folds, which tend to open at the exposed ends of the side seam folds.

The instant invention creates leak-proof capabitity within reasonable probability limits for single-ply bags under usual manufacturing conditions by: (a) in all three embodiments, completely filling the regions along 3,358,903 Patented Dec. 19, 1967 the bottom corners with extra sealing material, (b) in two embodiments, decreasing the probability of a leak caused by a random skip in adhesive application by depositing a secondary line of adhesive in back-up position to the primary line of adhesive which is in contact with bag contents, and (c) in two embodiments, stressrelieving the primary line of adhesive along a side seam by transferring crosswise tensile stresses to the secodary line of adhesive which is shielded from contact with contents of the bag. A multi-ply embodiment is also shown that uses the side-seam construction of one of the singleply embodiments.

The primary line of adhesive in this invention is generally applied to form a primary peel joint which may project inwardly or outwardly and in all embodiments shields the secondary line of adhesive from the bag contents. The secondary line of adhesive is applied to form a secondary shear joint along at least one bag wall in parallel to tht primary peel joint in the three single-ply embodiments of this invention that are shown in the drawings. In two of the embodiments, the secondary shear joint entirely sustains transversely-applied loads, thus protecting the primary peel joint. In the third embodiment, the primary peel joint is converted to a shear joint that sustains transversely-applied loads in series with the secondary shear joint.

Each embodiment is shown on a separate sheet of drawings. FIGURES 1 through 6 show a tape embodiment having tape-protected primary seams. Each primary seam is formed by evenly mating the edges of the opposed side walls to make a peel joint which is protected by an overlapping tape that is adhesively joined in shear to the outer surfaces of both wall members on the tension sides of said peel joint, whereby the tape sustains all transverse tensile loads through shear joints that are shielded from the bag contents and that function as secondary leakage barriers. Thus, secondary lines of adhesive holding the tape to wall members of the bag form a pair of shear joints straddling the peel joint. Each shear joint is normally shielded from the bag contents but can function as a back-up seal for the peel joint. The peel joint formed by the primary line of adhesive is completely protected from transverse tensile stresses.

FIGURES 7 through 12a show an overlap embodiment wherein the primary seam is initially formed by adhesively conjoining opposed wall members to make an outwardly-projecting peel joint, with one wall member extended past the peel joint as a flap, and wherein the secondary seam is formed by overlapping said flap against the other wall member and adhesively conjoining said flap and said wall member to make a shear joint that sustains transverse tensile forces. The secondary shear joint is normally shielded from the contents of the bag but can function as a back-up seal for the peel joint.

FIGURES 13a through l-8b show a lap embodiment wherein the primary seam is formed by evenly mating the inner surfaces of the opposed side walls to make an outwardly projecting peel joint that is changed to a shear joint by lapping said primary seam against the outer surface of one side wall and adhesively conjoining the juxtaposed surfaces to form a secondary seam as a shear joint that sustains transverse tensile forces in series with the primary seam. The secondary shear joint is completely shielded from the contents of the bag.

FIGURES 19 through 24b show the lap embodiment of FIGURES 13a through 18b for two-ply bags.

FIGURE 1 is a plan view of the blank from which the tape embodiment of the bag is made, with longitudinal fold lines indicated.

FIGURE 2 is a plan view of the blank shown in FIG- URE 1 after folding. Twin lines of adhesive have been applied longitudinally along each flap from one end (corresponding to a top edge of the finished bag) to, and slightly past, the transverse fold line (corresponding to the bottom of the finished bag before filling).

FIGURE 3 is a plan view of the blank shown in FIG- URE 2 with a longitudinally folded tape placed on top of the'outer line of adhesive and with another line of adhesive on the tape.

FIGURE 4a is a side view of FIGURE 3, looking in the direction of the arrows 4a4a in FIGURE 3, and shows the folded tape on each flap.

FIGURE 4b is a cross-sectional enlargement of the indicated area in FIGURE 3, looking in the direction of the arrows 4b-4b in FIGURE 3.

FIGURE 5 is a perspective view of a finished bag, as if tightly filled, which shows a bottom flap through the cutaway area.

FIGURE 6a is a perspective view of a finished bag, as if empty.

FIGURE 6b is an enlarged cross-sectional view of the joints in a side seam looking in the direction of the arrow 6b-6b in FIGURE 6a.

FIGURE 7 is a plan view of the blank needed for the overlap embodiment of the invention. Longitudinal fold lines are indicated which delineate recessed flaps.

FIGURE 8 shows the blank of FIGURE 7 after longitudinally folding the recessed flaps beneath the blank, with additional longitudinal fold lines indicated and with V-shaped lines of adhesive applied on each side of the transverse fold line.

FIGURE 9 shows the plan view of FIGURE 8 after longitudinally folding a second time, thereby exposing the recessed flaps of FIGURE 7, and applying twin lines of adhesive along the wider part of these flaps from one end (corresponding to a top edge of the finished bag) to the transverse fold line and slightly beyond.

FIGURE 10a is a side view of FIGURE 9, looking in the direction of the arrows 10a-10a in FIGURE 9.

FIGURE 10b is an enlarged cross-sectional view of the blank of FIGURE 9, looking in the direction of the arrows 10b-10b in FIGURE 9.

FIGURE 11 is a perspective view of a finished bag, as if tightly filled, with a bottom corner flap shown through the cutaway area.

FIGURE 12 is a perspective view of a finished bag, as if empty, with one flap folded back to show the relationship of flaps and adhesive joints.

FIGURE 12b is an enlarged cross-sectional view of the joints in a side seam, looking in the direction of the arrows 12b-12b in FIGURE 12a.

FIGURE 13 is a plan view of the blank needed for this embodiment. Longitudinal fold lines and V-shaped lines of adhesive have been applied on each side of the bottom area.

FIGURE 14 shows the blank of FIGURE 13 after the longitudinal folds have been made, with single lines of adhesive applied to each flap, from one top edge to a position slightly past the center fold, and with additional secondary fold lines indicated.

FIGURE 15 is the plan view of FIGURE 14 after the secondary folds have been made and with additional adhesive applied to the flaps from one top edge to a position slightly past the center fold.

FIGURE 16 is a side view of FIGURE 15, looking in the direction of the arrows 16-16 in FIGURE 15.

FIGURE 17a is a perspective view of a finished bag, as if tightly filled, with a corner flap exposed through a cutaway portion.

FIGURE 17b is an enlarged cross-sectional view of the joints in a side seam, looking in the direction of the arrows 17b-17b in FIGURE 17a.

FIGURE 18a is a perspective view of the finished bag, with one fiap folded back to show the flap relationship along a side seam.

FIGURE 18b is an enlarged cross-sectional view of the 4 joints in a side seam, looking in the direction of the arrows 1Sb-18b in FIGURE 18a.

FIGURE 19 is a plan view of a two-walled blank needed to manufacture the embodiment shown in FIG- URES 13 through 18b in dual-Wall form. Longitudinal fold lines and V-shaped lines of adhesive have been applied to the uppermost ply on each side of the bottom area.

FIGURE 20 shows the blank of FIGURE 19 after the longitudinal folds have been made, with single lines of adhesive applied to each flap, from one top edge to the center fold, and with secondary longitudinal fold lines indicated.

FIGURE 21a shows the blank of FIGURE 20 after the secondary longitudinal folds have been made and with additional adhesive applied to the flaps from one top edge to a position slightly past the center fold.

FIGURE 21b is an enlarged crosssectional view of a flap area, looking in the direction of the arrows across line 21b-21b in FIGURE 21a.

FIGURE 22 is a right side view of FIGURE 21a.

FIGURE 23a is a perspective view of a finished bag.

FIGURE 23b is an enlarged cross-sectional view of a compound seam, looking in the direction of arrows 23b23b in FIGURE 23a.

FIGURE 24a is a perspective view of a finished bag, as if tightly filled.

FIGURE 24b is an enlarged cross-sectional view of a compound seam, looking in the direction of the arrows 24b-24b in FIGURE 24a.

The tape embodiment 20 shown in FIGURES I through 6b is formed from the bag blank shown in FIGURE 1, having ends 21 and side edges 22. Longitudinal score lines 24, that delineate side wall members 26 and front and back wall members 25, are added. The blank is folded along longitudinal score lines 24 to pro duce the folded blank shown in plan view in FIGURES 2 and 3 and in side view in FIGURE 4a. A bottom score line 23 is made transversely to longitudinal score lines 24 in the center of the bag blank.

Dual lines of adhesive 27, 28 are applied to the surface of the blank in parallel near each side edge 22. Both adhesive lines 27, 28 may be applied from one end 21 to bottom score line 23 and beyond through springback distance 34, as shown clearly in FIGURE 2. How ever, adhesive line 27, which is farther from edge 22, is preferably terminated about %-1 short of bottom score line 23, yet adhesive line 28 must be applied as shown in FIGURE 2.

It is necessary that springback distance 34 beyond bottom line 23 be at least equal to the longitudinal length of bag under stress because of bottom folding. This distance 34 is proportional to thickness and stiffness of the paper used.

A tape 29, doubled longitudinally upon itself, is applied upon each line of adhesive 27, as shown in FIGURES 3, 4a, and 4b, so that each line of adhesive 28 that is nearest to edge 22 is not covered. Tape 29 should not extend beyond adhesive line 27. Each line of adhesive 28 is the primary line of adhesive for forming an inwardlyprojecting primary peel joint, constituting the primary seam. Upon the exposed surface of folded tape 29, an additional line of adhesive 31 is applied from end to end.

The blank is then folded end-over-end about transverse score line 23 so that the primary lines of adhesive 28 and secondary lines of adhesive 27, 31 contact the opposed portions of side wall members 26 and form an inwardly projecting primary seam 30, on each side of front and back wall members 25, that is straddled by a pair of secondary seams of shear-joint type which are formed by secondary lines of adhesive 27, 31.

The bag thus produced is shown in FIGURE 6a in a slightly opened condition. FIGURE 6b shows the compound seam with primary seam 30, formed by primary line of adhesive 28, and the secondary shear joints formed by secondary lines of adhesive 27 and 31. FIGURE shows the tape embodiment 20 of the instant invention in its fully opened condition. At each side of the substantially flat bottom 33, a triangular corner flap 32 extends inwardly but is not necessarily joned to any surface of the bag.

The overlap embodiment 50 of this invention, shown in FIGURES 7 through 12b, is formed from the blank shown in FIGURE 7, having ends 51 and sides 63, 64 that are separated by transverse step 62. Close to sides 63, 64 are longitudinal score lines 52 that delineate overlap flap 65 and lap flap 66.

After flaps 65, 66 are folded beneath the blank, as shown in FIGURE 8, a second pair of longitudinal score lines 54 are made that delineate side wall members 56 and front and back wall members 55. A central bottom score line 53, transverse to longitudinal score lines 54,

is made, and a pair of V-shaped bottom adhesive lines 70 are added, each having a base on a score line 54 and a distance to apex equalling the transverse distance between score lines 52 and 54. The longitudinal distance between transverse bottom score line 53 and transverse step 62 equals springback distance 67 that is proportional to thickness and stiffness of the paper used.

The side wall members 56 are then folded on top of front and back wall members 55, as shown in FIG- URE 9, so that lap flap 66 and overlap flap 65 are uppermost, as shown in FIGURE 10a. Dual lines of adhesive 57, 58 are next applied onto overlap flap 65, from transverse step 62 to end 51, so that they straddle the end of flap 66, i.e., fiap 66, if extended, would be appproximately midway between adhesive lines 57, 58. These adhesive lines are clearly shown in FIGURE 10b. However, experience has shown that adhesive line 57, which is closer to side 63, is preferably terminated very slightly short of transverse bottom score line 53, with consequent movement of transverse step 62 to bottom score line 53. Primary adhesive line 58 must nevertheless be extended as shown through the springback distance 67 shown in FIGURE 9.

When the blank is folded end-over-end about fold line '53, adhesive line 58 forms primary seam 60 of peel-joint type, that is never allowed to assume a normal position midway between wall members 56 because it is held down by overlap flap 65 which is attached through a shear joint, formed by secondary line of adhesive 58, to the adjacent wall member 56.

The bag thus produced is shown in FIGURE 12a in slightly opened condition. FIGURE 12b shows the compound seam produced by the primary line of adhesive 58 forming a peel joint 60 which protects a shear joint, formed by secondary line of adhesive 57, from the bag contents. FIGURE 11 shows bag made according to the overlap embodiment 50 in fully opened condition. At each side of the substantially flat bottom 63, a triangular corner flap 62 is fastened to bottom 63 with V- shaped adhesive lines 70.

The lap embodiment 80 of this invention, shown in FIGURES 12 through 18b, is formed from the blank shown in FIGURE 13 that has ends 81 and straight side edges 93. Longitudinal score lines 84 delineate front and back walls 86, 85. Along transverse central bottom score line 83, V-shaped bottom adhesive lines 100, each having a distance to apex that is less than the transverse distance between a longitudinal score line 84 and edge 93, are added inwardly of each score line 84.

After folding upwardly along score lines 84, as shown in FIGURE 14, longitudinal score lines 82 are made in each flap produced, delineating side wall members 86 between score lines 84 and 82. A secondary line of adhesive 87 is added longitudinally onto each flap from one end 81 to center fold line 83 and slightly beyond. Each edge flap 95 is then folded onto side wall members 86, and a primary line of adhesive 88 is added onto each flap 95 from one end 81 to the center fold line 83 and 6 a springback distance 94 beyond. This distance 94 should be no less than the springback distance which is characteristic for the paper forming each wall member 86.

The blank is then folded end-over-end about score line 83 so that each flap 95, having primary line of adhesive 87 on one side and secondary line of adhesive 88 on the other side, is pressed between adjacent wall members 86 to form back-to-back shear joints, as shown clearly in FIGURES 16b and 17b.

The bag thus produced is shown in FIGURE 18a in slightly opened condition, with the compound seam formed of back-to-back shear joints shown in FIGURE 18b. FIGURE 17a shows the bag made according to the lap embodiment of the invention in fully opened condition. At each side of the substantially fiat bottom 103, a triangular corner flap 92 is fastened to bottom 103 with V-shaped adhesive lines 100.

The two-ply lap embodiment, shown in FIGURES 19 through 24b, is formed from the two-ply blank shown in FIGURE 19 that has ends 111, 111', and straight side edges 123, 123'. Dual lines of adhesive 127, 128 conjoin the plies near edges 123, 123'. Inward adhesive lines 128 reinforce outward adhesive 127 and diffuse transverse stresses. Longitudinal score lines 84 delineate front and back walls 116, 116', 115, 115'. Along transverse central bottom score line 113, V-shaped bottom adhesive lines 130, each having a distance to apex that is substantially equal to the transverse distance between a longitudinal score line 114 and edge 113, are added inwardly of each score line 114.

After folding upwardly along score lines 114, as shown in FIGURE 21a, longitudinal score lines 112 are made in each flap produced, delineating side wall members 116, 116 between score lines 114 and 112. A secondary line of adhesive 117 is added longitudinally onto each flap from one end 111, 111 to center fold line 113. Each edge flap 125 is then folded onto side wall members 116, and a primary line of adhesive 118 is added onto each edge flap 125 from one end 111, 111 to the center fold line 113 and a springback distance 124 beyond. This springback 124 depends upon the stiffness of the multiply wall members 116, 116'. Inward adhesive lines 128 may be omitted on the side of the blank beneath primary adhesive line 118 as seen in FIGURE 21a, so that they extend only from the top edge 111, 111' of the finished bag to the central bottom score line 113.

The blank is then folded end-over-end about score line 113 so that each flap 125, having primary line of adhesive 117 on one side and secondary line of adhesive 118 on the other side, is pressed between adjacent wall members 116, 116' to form back-to-back shear joints, as shown clearly in FIGURES 21b, 22, and 24b.

The bag thus produced is shown in FIGURE 23a in slightly opened condition, with the compound seam formed of back-to-back shear joints shown in FIGURE 23b. FIGURE 24a shows the bag made according to the lap embodiment of the invention in fully opened condition. At each side of the substantially flat bottom 113, a triangular corner flap is fastened to bottom 133 with V-shaped adhesive lines 130.

The very similar construction shown in FIGURES 19 through 2417 is particularly noteworthy for the dual interply lines of adhesive 127, 128 that hold plies and 115' together. As shown in FIGURE 19, these adhesive lines 127, 128 can be extended from one end 111, 111' to the other, but it is often satisfactory if inner lines 128 are extended only halfway, to transverse central bottom score line 113.

Any of the secondary lines of adhesive of the secondary seams can be a water-resistant adhesive, but the primary lines of adhesive of the primary seams must be a waterproof adhesive if the bag is to be leakproof toward aqueous contents.

Bags of these three single-ply embodiments 20, 50, 80

can be leak-resistant or leak-proof, depending upon'treatment of the paper forming the blank. If the paper is simply treated for water resistance, there will be no leakage through seams, but a small amount of water can pass through the paper walls. If the paper is made waterproof, as by coating with an impervious film, such as polyethylene, there will be substantially no leakage. Seventeen inches of water, for example, has been successfully maintained in a suspended bag made of water-proof paper.

We claim:

1. A paper bag with leak-proof capability that has a seamless bottom and a leak-proof compound seam along each side, each compound seam comprising:

(a) a primary seam of peel-joint type-that is formed by adhesively conjoining the edges of opposed bag walls, the adhesive being exposed to the interior of the bag and the seam being protected from transversely applied loads, and

(b) a secondary seam of shear-joint type that is parallel to the primary seam and is formed by adhesive juncture with a bag wall on the tension side of the primary seam, the adhesive being shielded from the interior of the bag by the primary seam, said secondary seam being capable of functioning as a secondary leakage barrier and of entirely sustaining transversely applied loads.

2. The paper bag of claim 1 wherein a secondary seam is on each side of each primary seam, said secondary seam being formed by an overlapping tape that straddles the primary seam and is adhesively joined in shear to the outer surfaces of both bag walls on the tension sides of the primary seam, whereby the tape and the secondary seams are capable of cooperatively functioning as a secondary leakage barrier.

3. The paper bag of claim 1 wherein said primary seam projects outwardly with the edge of one bag wall extending substantially past the edge of the other bag Wall as a flap that is adhesively joined to the other bag wall on the tension side of the primary seam to form the secondary seam and enclose the primary seam, whereby the flap and the secondary seam are capable of cooperatively functioning as a secondary leakage barrier.

4. A multi-ply paper bag that has a seamless bottom and a leak-proof compound seam along each side, each compound side seam comprising:

(a) an outwardly projecting primary seam of peeljoint type that is formed by adhesively conjoining the evenly mated inner surfaces of the opposed side walls, the adhesive being exposed to the interior of the bag,

(b) an outward adhesive line that conjoins adjacent plies in back-to-back relationship with said primary seam and on each side thereof,

(0) a secondary seam of shear-joint type that is shielded from the interior of the bag by said primary seam and is formed by lapping said outwardly projecting primary seam against the outer surface of one bag wall and adhesively conjoining the juxtaposed surfaces, whereby the primary seam is converted to shear-joint construction in back-to-back relationship to the primary seam and sustains transversely applied loads in series with the secondary seam, and

(d) an inward adhesive line, for diifusing transverse stresses, that conjoins adjacent plies of the side wall in back-to-back relationship to the secondary seam.

References Cited UNITED STATES PATENTS 160,991 3/ 1875 Amazeen 229-61 2,203,726 6/ 1940 Hellema 2296l 2,325,673 8/ 1943 Gul'wick 229-53 3,269,642 8/1966 Cvacho 229-5 3 FOREIGN PATENTS 580,518 9/ 1946 Great Britain.

DAVID M. BOCKENEK, Primary Examiner. 

1. A PAPER BAG WITH A LEAK-PROOF CAPABILITY THAT HAS A SEAMLESS BOTTOM AND A LEAK-PROOF COMPOUND SEAM ALONG EACH SIDE, EACH COMPOUND SEAM COMPRISING: (A) A PRIMARY SEAM OF PEEL-JOUNT TYPE THAT IS FORMED BY ADHESIVELY CONJOINING THE EDGES OF OPPOSED BAG WALLS, THE ADHESIVE BEING EXPOSED TO THE INTERIOR OF THE BAG AND THE SEAM BEING PROTECTED FROM TRANSVERSELY APPLIED LOADS, AND (B) A SECONDARY SEAM OF SHEAR-JOINT TYPE THAT IS PARALLEL TO THE PRIMARY SEAM AND IS FORMED BY ADHESIVE JUNCTURE WITH A BAG WALL ON THE TENSION SIDE OF THE PRIMARY SEAM, THE ADHESIVE BEING SHIELDED FROM THE INTERIOR OF THE BAG BY THE PRIMARY SEAM, SAID SECONDARY SEAM BEING CAPABLE OF FUNCTIONING AS A SECONDARY LEAKAGE BARRIER AND OF ENTIRELY SUSTAINING TRANSVERSELY APPLIED LOADS. 